The present invention relates to a closed scroll compressor apparatus in which the inside of a closed container is kept at a discharge pressure, and more particularly, to cooling and lubricating systems thereof.
In a closed scroll compressor apparatus, a scroll compression mechanism unit serving to compress gas and a motor for rotatably driving the scroll compression mechanism unit are encased in a closed container, and lubricating oil is stored in a lower part of the closed container and supplied through an oil supply passage formed in a crank-shaft of the scroll compression mechanism unit to the scroll compression mechanism unit and bearings. On the other hand, compressed gas is discharged in the closed container and supplied to required portions through a discharge port formed at a position located between the scroll compression mechanism unit and the motor, the motor being cooled by the discharge gas thus passing through the closed container.
As described above, since the discharge port is provided between the scroll compressor mechanism unit and the motor, the gas discharged from the scroll compression mechanism unit flows out to the outside of the closed container without passing through a space below the motor in a vertical type compressor apparatus or without passing through a space on the opposite side to the scroll compression mechanism unit with respect to the motor in a horizontal type compressor apparatus. A problem rises in that portions located in these spaces cannot be cooled sufficiently. To solve this problem, it is considered to operate the scroll compression mechanism unit at high speed to increase the velocity of the discharge gas or to form the discharge port at a position located on the opposite side to the scroll compression mechanism with respect to the motor. However, the former method has a problem that the lubricating oil contained in the discharge gas is not separated but discharged through the discharge port, resulting in that the lubricating oil in the closed container is reduced. According to the latter method, the lubricating oil is discharged to the outside of the closed container together with the discharge gas to bring about a shortage of the lubricating oil in case of the vertical type compressor. In case of the horizontal type compressor, the lubricating oil stored in the lower part of the closed container is made to flow toward the discharge port due to a pressure difference in the closed container, resulting in the shortage of the lubricating oil along the oil supply passage and hence the insufficient lubrication. This adverse condition becomes more noticeable at high speed operation. For this reason, the scroll compressor apparatus of the prior art is operated at a relatively low speed and formed with the discharge port at the above-mentioned position although the cooling effect cannot be achieved satisfactorily.
In order to lubricate every portion of the compressor apparatus sufficiently, it is better that a large quantity of lubricating oil be stored in the closed container. However, with a large stored quantity of lubricating oil in the lower part of the closed container, a rotor of the motor stirs the lubricating oil, resulting in the loss of power of the motor. For this reason, the lubricating oil is permitted to be stored only up to the lower end of the rotor. In other words, to store a large quantity of lubricating oil, it is necessary to increase the size of the closed container.
Further, in the compressor apparatus of the type that the lubricating oil is stored in the closed container, when the compressor apparatus is brought to a halt, the pressure in the closed container is somewhat lowered so that the discharge gas dissolves in the lubricating oil stored in the closed container. As a result, when the compressor apparatus is restarted, the discharge gas thus dissolved results in foaming. Upon occurrence of the foaming, foamed lubricating oil is supplied to the bearings, resulting in an insufficient supply of the lubricating oil to the bearings resulting in a potential bearing seizure.
On the other hand, in case of the horizontal type compressor apparatus, since a stator of the motor is partially submerged in the lubricating oil stored in the lower part of the closed container, there is a possibility that the sheath of wire of the stator is damaged by iron dust or the like contained in the lubricating oil to cause a burnout of the stator.
In addition, a variable capacity scroll compressor apparatus comprises a plurality of closed scroll compressors which are connected in parallel manner to a common suction pipe and a common discharge pipe, and a plurality of oil equalizing pipes through which lower parts of the closed containers of the respective compressors are communicated with each other for equalizing the quantities of lubricating oil stored in the closed containers. In the variable capacity scroll compressor apparatus, the overall capacity is controlled by making inoperative some of the plural compressors. This variable capacity scroll compressor apparatus has the following problems in addition to the disadvantages described above.
When all the compressors are operated, internal pressures in the closed containers of all the compressors are not substantially equalized with each other due to the manufacturing differences among the individual compressors, pipes and the like. For this reason, the quantity or lubricating oil in each compressor is not uniform, thereby causing nonuniform distribution of the lubricating oil among the compressors. As a result, the compressor which is lacking in lubricating oil is not lubricated sufficiently, thereby resulting in bearing seizure. Meanwhile, when the compressor apparatus is operated in a capacity controlling mode in which some of the compressors are made inoperative, since the internal pressure in the closed container of the inoperative compressor is lower than that of the compressor which is in operation, the lubricating oil flows from the compressor in operation into the inoperative compressor, thereby causing non-uniform distribution of the lubricating oil. Further, there is a problem that a part of discharge gas compressed by the compressor in operation flows into the inoperative compressor and dissolves in the lubricating oil in the inoperative compressor to dilute the lubricating oil. In addition, when the inoperative compressor is started again, there is a problem that the discharge gas thus dissolved results in foaming.